Isatis tinctoria • Class A

This biennial or short lived perennial grows from 1 to 4 feet tall with a 3 to 5 foot long taproot.

The basal leaves at the stem base are stalked, bluish green, and covered with fine hairs. Stem leaves leaves are lnace shaped, alternate, 1 to 7 inches long, with a whitish mid vein and not stalk.

When the rosette bolts, up to 20 stems can be produced. Its small yellow flowers bloom from April to June and are cross shaped with 4 sepals, 4 petals, 6 stamens. Flowers are found in clusters on the branch tips.

Dyer's Woad is a very aggressive weed with the ability to form a monoculture and is non-palatable. Rotting seed pods contain a chemical with allelopathic properties that limits the root development of surrounding plants and allows D.W. to outcompete other plants.

Dyer's Woad will establish in rocky soils, along road sides, gravel pits, levees and railroad rights-of-ways. From there it has the ability to spread by seed to well vegetated pastures, forests, waterways, hayfields and crop lands. 

Dyer's woad was used as a source for blue dye (indigo) since the 13th century and it was cultivated till the 1930’s in England. Indigotine, the blue dye chemical, is located in the leaves. 
 

• Mowing is not considered an effective treatment due to re-sprouting from the crown.

• Hand pulling can be very effective in reducing infestations. It is critical to remove the crown to prevent re-sprouting. Hand pulling is easiest after the plants have bolted, but should be done before seed set. Most hand pulling programs have indicated it is necessary to follow up for several years to prevent re-infestation.

• The selective, translocated active ingredient 2, 4-D (used in Weedmaster) is the most effective treatment. Plants should be treated in the seedling to rosette stages. Late season control of flowering plants is difficult and may not eliminate seed production. 

• To minimize any harmful impact on bees and other pollinators, timing is important.  Ideally, treat plants before blooming.  If treatment after blooming is necessary, do control work early in the morning, or in the evening when bees are less active.

• A native rust pathogen is effective in preventing seed or fruit production and seems to be spreading naturally to new populations.  For information about the biological control of this or any other noxious weed, see the WSU Extension Integrated Weed Control Project   

For more information on this noxious weed Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photos by Rebecca Shoemaker, Pierce County Noxious Weed Control Board.